Type 48 series is the main transmitting set for heavy ships and cruisers and replaces the Type 36S. It is a high power set.

The set has four power boards which carry the necessary switches, fuses and instruments for the distribution of power to the set and W/T office. The transmitting circuits are carried in eight main valve panels which face the power boards and the rectifying and smoothing panels which are fitted in a convenient position inside the safety cage. A small panel containing the H/F neutralised condensers, etc, is secured to the back of the H/F main transmitting panel. The switches necessary for the control of the set are assembled in "Board 2S Controlling" which is mounted on a stand and fitted in the CRR (central receiving room) (note, the silent cabinet, used from the very earliest of days -see PRE WW1 FILES - is no longer fitted/used).

This was the first set with a MASTER OSCILLATOR which had a single controlling valve and was the primary means of producing the oscillations - All the Components of the H/F Master Circuit are enclosed in an earthed copper screening box supported by springs in Panel 3S H/F Master. The set was also fitted with the then conventional (all previous sets) Self Excitation which was used when and if the Master Oscillator became un-useable. The waveform characteristics were shown as follows:-

The L/F Master circuit is disconnected from the main transmitter and used as the Low Power transmitter, connected direct to the aerial via a contact arm of the L/F circuits change over switch (COS). Under Further Reading look at the file Type 48 Low Power Set which simply shows the working of the Type 48 Low Power Set.

This transmitter was capable of high speed Morse transmission and used Grid Signalling to achieve this. This necessitated HT to the main amplifying and master circuit valves being made continuously. Put simply, when the Morse is being sent (key down = 'marking' or mark condition) the aerial absorbs the resultant 'oscillatory signal' but when the transmitter is 'spacing' (key up = nothing being sent) the valves themselves were designed to absorb the 'non-oscillating' condition of the transmitter. Under Further Reading look at the file Type 48 Grid Signalling and Absorbing which shows how the transmitter coped with the 'marking' and 'spacing' conditions.

In direct association with high speed transmission, came the need to self-check for the accuracy of transmission. Under Further Reading look at the file 48 Self Monitoring which shows a simple diagram to control that event, and note the undulator, a high speed automatic Morse keyer/sender.

Under Further Reading also look at the following files:
For a complete view of the Type 48 schematic look under at the file Type 48 Overall Schematic.
Look at the Aerial Circuits an Protection Circuits file to see the all important big ship aerial circuits and the protection of receivers sited in offices remote from the main W/T office which use the aerials.
The file Type 48 Aerial System shows one of the aerial systems.
Look at Type 48 Auxiliary Switching Circuits for details on the auxiliary switching circuits which we can liken to the traffic lights of a large and complex transmitter system. These include the transmitter type used, its emission, its aerial, its protection circuits (equipment and personnel) etc.